1. Technical Field of the Invention
The present invention relates to temperature alarm circuitry, and more particularly to a test mode and method useful with respect to a temperature alarm circuit and a tamper detection circuit.
2. Description of Related Art
There exist electronics systems in which very sensitive data may be stored in an integrated circuit (IC). For example, some portable credit card scanners store credit card data in volatile memory which, if pilfered, would potentially expose credit card holders to credit card fraud.
In an effort to prevent such pilfering of data, techniques exist for detecting when an IC or system is being tampered with, and destroying the stored data in response to the detection. In this way, sensitive data stored in such systems remains inaccessible.
One known way of attempting to improperly access stored data is to subject the IC or system to changes in temperature, for example by exposing the IC or system to extreme heat or extreme cold. There is accordingly a need for a type of tamper detection which involves detecting whether the temperature of the IC or system falls outside an expected operating range (for example, too hot or too cold in comparison to certain temperature thresholds, wherein the expected operating range falls between the high and low thresholds), and asserting an alarm responsive to such detection. Such a temperature tamper detector would serve the purpose of preventing a tamperer from accessing stored, sensitive data in part by the tamperer changing the operating temperature of the IC or system.
The best way to test operation of the temperature tamper detector is to subject the detector itself, or the IC or system within which the detector is installed, to a temperature which is outside the expected operating range (i.e., an extreme temperature). If the detector output is monitored and it changes state in response to the applied extreme temperature, then one can assume that the temperature tamper detector has been programmed and is operating properly. This testing solution, however, is not particularly practical or economical since it necessitates the generation of an extreme temperature (too hot or too cold) outside the expected operating range followed by the exposure of the detector, IC or system to that extreme temperature. In some testing instances it may be impossible or inconvenient to generate the required extreme temperature for performing the test. There is a need in the art to be able to test operation of the temperature tamper detector at a more readily available and convenient temperature, such as room temperature, which lies within the expected operating temperature range.